Currently, a quantum dot type semiconductor device using quantum dots is actively researched. As one of the quantum dot type semiconductor devices, there is a quantum dot infrared photodetector (QDIP) which is operated by exciting carriers confined in quantum dots when being irradiated with infrared rays so as to be detected as a photoelectric current. Regarding a structure of the QDIP, various researches are conducted.
As an infrared detector which realizes desired long wavelength characteristics and has a low dark current and a high sensitivity, a structure in which an upper part and a lower part of quantum dots are covered with a barrier layer such as AlAs is proposed. However, in this case, impurities are incorporated into the quantum dots due to Al of the barrier layer at the time of forming the quantum dots, and an impurity level is formed in the quantum dots. Therefore, there is a problem in that noise increases and an S/N ratio decreases when detecting infrared rays.
The followings are reference documents.    [Document 1] Japanese Laid-open Patent Publication Nos. 2009-65141,    [Document 2] Japanese Laid-open Patent Publication No 2012-195333, and    [Document 3] Japanese Laid-open Patent Publication No 2016-136585.